JP2010188234A - Electrostatic coating apparatus and electrostatic coating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic coating apparatus capable of obtaining high smoothness for the appearance of a coated surface. <P>SOLUTION: A clear coating facility includes: a coating material supply pipe 41 and a gear pump 43 for supplying a coating material; a solvent supply pipe 42 and a solvent discharger 44 for supplying a solvent; a static mixer 45 for mixing the coating material supplied from the coating material supply pipe 41 and the gear pump 43 and the solvent supplied from the solvent supply pipe 42 and the solvent discharger 44; a coating gun 30 for spraying the coating material and the solvent mixed by the static mixer 45; and a control device 50 for controlling them. The control device 50 drives the solvent discharger 44 to adjust the supply amount of the solvent so that the NV value of a coated film formed on a coated surface falls within a predetermined range. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an electrostatic coating apparatus and an electrostatic coating method. Specifically, the present invention relates to an electrostatic coating apparatus and an electrostatic coating method for electrostatically coating a surface to be coated.

2. Description of the Related Art Conventionally, a 3-coat 3-bake method is known as a method for painting a car body. The 3-coat 3-bake method is a method in which electrodeposition coating, baking, intermediate coating, baking, base coating, clear coating, and baking are performed in this order.
In the above coating process, for example, a rotary atomizing coating apparatus is used as a coating apparatus. The rotary atomizing coating apparatus rotates while applying a high voltage to the rotary atomizing head, and supplies liquid paint to the rotary atomizing head in this state. As a result, the liquid paint is charged and atomized, and sprayed from the leading edge of the rotary atomizing head to perform electrostatic coating.

  By the way, high-grade vehicles are required to have high smoothness in the appearance of the vehicle. For this reason, when painting the body of a luxury car, it is common to perform a water sharpening process after the intermediate coating process. This water sharpening step is a step of manually polishing with a sander or the like while applying water to the vehicle body.

  However, when the water sharpening process is carried out, it takes time for the worker to become proficient, and there is a problem that the cost for arranging the worker is increased and the manufacturing cost of the automobile is increased.

  Here, a technique for maintaining the finish of the painted surface has been proposed. That is, a technique has been proposed in which the finish of the painted surface is kept constant by adding various solvents to the paint according to the paint temperature, paint viscosity, and booth temperature (see Patent Document 1). Specifically, the solvent is stored in a thinner tank, and the solvent is pumped to the paint tank with a pump.

JP-A-6-277574

However, as for the paint tank with a large capacity as in the above document, the supply accuracy of the general-purpose pump is sufficient as a means for supplying the solvent, but the paint tank is installed at a place away from the paint booth via the circulation pipe. Therefore, a large amount of paint adjusted with thinner cannot instantaneously follow changes in the paint booth environment.
Thus, for example, a method of adjusting the paint thinner in the vicinity of the paint gun can be considered. In this case, the amount of paint supplied to each paint gun is small, and the amount of thinner mixed with the paint is also extremely small. Therefore, it becomes difficult for the general-purpose pump to control supply of a very small amount of thinner. That is, if the amount of the thinner is too large, sagging occurs, resulting in a coating defect. If the amount of the thinner is too small, the coating particles may lose fluidity before they become familiar with the surface to be coated, and unevenness may remain on the painted surface.

  In particular, this problem becomes significant when the side surfaces of the vehicle body are painted. In other words, when painting the upper surface of a vehicle body such as a bonnet or roof, even if paint particles are applied to the surface to be coated and unevenness occurs, gravity acts perpendicularly to the surface to be coated. Thus, the paint particles are easily adapted to the shape of the surface to be coated. However, when painting the side of a vehicle body such as a fender or a door panel, if the paint particles are applied to the surface to be coated and unevenness occurs, gravity acts along the surface to be coated. However, it becomes difficult to adapt to the shape of the surface to be painted.

  An object of this invention is to provide the electrostatic coating apparatus and electrostatic coating method which can obtain high smoothness about the external appearance of a coating surface.

  The electrostatic coating apparatus (for example, a clear coating facility 10 described later) of the present invention includes a paint supply means (for example, a paint supply pipe 41 and a gear pump 43 described later) for supplying paint and a solvent supply means (for example, paint supply pipe 41 and gear pump 43 described later) A solvent supply pipe 42 and a solvent extruder 44), which will be described later, and a mixing means (for example, a static mixer 45, which will be described later) for mixing the paint supplied from the paint supply means and the solvent supplied from the solvent supply means. A static atomizing coating apparatus (for example, a coating gun 30 described later) for spraying the paint and solvent mixed by the mixing means, and a control means (for example, a control apparatus 50 described later) for controlling them. In the electrocoating apparatus, the control means drives the solvent extruding means so that the NV value of the coating film formed on the surface to be coated (for example, a body 20 described later) falls within a predetermined range. As such, and adjusting the supply amount of the solvent.

  Here, the solvent to be supplied may be a diluting solvent used for diluting the paint, but a high boiling point solvent is preferable because a high effect can be obtained with a smaller amount.

Further, the NV (Non Volatile) value is represented by the following equation, for example.
NV = (mass of paint after drying) / (mass of paint before drying) × 100

  According to the present invention, the solvent supply means is adjusted by driving the solvent extrusion means so that the NV value of the coating film formed on the surface to be coated falls within a predetermined range. By keeping the NV value of the coating within a predetermined range, the properties of the mixed paint can be controlled, so that the fluidity of the paint applied to the surface to be coated can be secured, and the appearance of the painted surface is highly smooth. Can be obtained.

  In this case, the solvent supply means is a cylinder type solvent extrusion apparatus (for example, a solvent to be described later) in which a piston (for example, a piston 442 to be described later) driven by a servo motor (for example, a servo motor 443 to be described later) is provided. It is preferable to include an extrusion device 44).

  There is no problem in mixing paint and various solvents in a large-capacity tank such as a paint circulation tank as in the past, but in order to prepare diluted paint in large quantities, it can quickly follow changes in booth temperature etc. Is difficult. Therefore, it is conceivable to mix the solvent and the diluted paint in the vicinity of the coating apparatus in the booth. In this case, since the properties of the coating sufficiently change with a small amount of solvent, a pump that quantitatively discharges the small amount of solvent is required. There is a gear pump as a pump that quantitatively supplies paint, but it is difficult to quantitatively supply a very small amount of solvent with this gear pump.

  That is, in the gear pump, when the discharge amount is reduced, it is difficult to control the discharge amount with high accuracy. Therefore, it is difficult to quickly manage the properties of the paint without waste, and it may be impossible to obtain the desired smoothness with respect to the appearance of the painted surface.

Therefore, according to the present invention, the solvent is supplied using a cylinder-type solvent extrusion apparatus in which a piston driven by a servo motor is provided. Since the solvent extrusion device has a structure capable of controlling a small discharge amount with high accuracy, the properties of the paint can be managed reliably.
Further, even if the solvent to be supplied is a high boiling point solvent, the solvent extrusion apparatus can control the low discharge, so there is no problem.

  The electrostatic coating method of the present invention mixes paint supply means for supplying paint, solvent supply means for supplying solvent, paint supplied from the paint supply means, and solvent supplied from the solvent supply means. An electrostatic coating method for electrostatic coating using a mixing unit and a rotary atomizing coating apparatus that sprays a paint and a solvent mixed by the mixing unit, wherein the solvent extrusion unit is driven to be coated The supply amount of the solvent is adjusted so that the NV value of the coating film formed on the surface is within a predetermined range.

  In this case, the solvent supply means includes a cylinder type solvent extrusion device in which a piston (for example, a piston 442 described later) driven by a servo motor (for example, a servo motor 443 described later) is provided. Is preferred.

  According to the present invention, the solvent extrusion apparatus is driven to adjust the supply amount of the solvent so that the NV value of the coating film formed on the surface to be coated falls within a predetermined range. By keeping the NV value of the coating within a predetermined range, the properties of the mixed paint can be controlled, so that the fluidity of the paint applied to the surface to be coated can be secured, and the appearance of the painted surface is highly smooth. Can be obtained.

1 is a plan view of a part of a coating line to which an electrostatic coating apparatus according to an embodiment of the present invention is applied. It is a perspective view of the clear coating equipment which comprises the coating line which concerns on the said embodiment. It is a schematic diagram which shows the path | route of the coating material and solvent of the clear coating equipment which concerns on the said embodiment. It is a figure which shows the relationship between the command value of discharge amount, and a measured value about a gear pump and a solvent extrusion apparatus. It is a 1st schematic diagram for demonstrating operation | movement of a clear painting installation. It is a 2nd schematic diagram for demonstrating operation | movement of a clear painting installation. It is a 3rd schematic diagram for demonstrating operation | movement of a clear painting installation. It is a 4th schematic diagram for demonstrating operation | movement of a clear painting installation. It is a 5th schematic diagram for demonstrating operation | movement of a clear painting installation. It is a 6th schematic diagram for demonstrating operation | movement of a clear painting installation. It is a figure which shows the relationship between the rotation speed of a rotary atomization head, and NV value. It is a figure which shows the relationship between the rotation speed of a rotary atomization head, and LW value. It is a schematic diagram which shows the path | route of the coating material and solvent of the clear coating equipment which concerns on the modification of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a plan view showing an outline of a part of a coating line 1 to which an electrostatic coating method according to an embodiment of the present invention is applied.
The painting line 1 performs top coating (base coating and clear coating).
FIG. 1 shows a part of a painting line 1, and this painting line 1 includes a base painting facility 3, a flash-off facility 4, an electrostatic along a conveyance path 2 along which a vehicle body 20 is conveyed. Clear coating equipment 10 as a coating device and baking equipment 5 are provided in this order.

  The base coating facility 3 is a facility that performs base coating on the intermediate coating on the body 20 as a painted surface, and the flash-off facility 4 is a facility that performs flash-off after the base coating. The clear coating facility 10 is a facility that performs clear coating on the body 20 after performing flash-off, and the baking facility 5 is a facility that performs baking of top coating (base coating and clear coating).

FIG. 2 is a perspective view of the clear painting facility 10.
The clear painting facility 10 includes six painting robots 11 to 16 provided on both sides of the conveyance path 2, a paint supply pipe 41 as a paint supply means for supplying paint to each of the painting robots 11 to 16, A solvent supply pipe 42 is provided as a solvent supply means for supplying a solvent to the paint supply pipe 41 connected to the coating robots 13 to 16 (see FIG. 1).
The painting robots 11 and 12 are upper surface painting robots that are disposed on the most upstream side with the conveyance path 2 interposed therebetween and paint the upper surface of the body 20.
The painting robots 13 and 14 are side painting robots that are arranged on the downstream side of the painting robots 11 and 12 with the conveyance path 2 interposed therebetween and paint the side surface of the body 20.
The painting robots 15 and 16 are side painting robots that are disposed on the downstream side of the painting robots 13 and 14 with the conveyance path 2 interposed therebetween and paint the side surface of the body 20.

  Each of the coating robots 11 to 16 includes a coating gun 30 as a rotary atomizing coating apparatus that sprays paint, and a robot arm 40 that adjusts the position of the coating gun 30 in a three-dimensional space.

FIG. 3 is a schematic diagram showing a detailed structure of the painting robots 13 to 16 of the clear painting facility 10.
The clear coating equipment 10 is supplied from a gear pump 43 as a paint supply means for supplying paint, a solvent extrusion device 44 as a solvent supply means for supplying solvent, and a paint and solvent extrusion apparatus 44 supplied from the gear pump 43. A static mixer 45 as mixing means for mixing the solvent and a control device 50 as control means for controlling them are provided.

The paint supply pipe 41 described above is connected to the paint gun 30 of the paint robots 13 to 16, and the gear pump 43 and the static mixer 45 are provided in the middle of the paint supply pipe 41.
The solvent supply pipe 42 described above is connected to a static mixer 45, and the solvent extrusion device 44 is provided in the middle of the solvent supply pipe 42. Valves 421 and 422 are provided on the upstream side and the downstream side of the solvent extrusion device 44 of the solvent supply pipe 42.
The coating gun 30 described above sprays the paint and solvent mixed by the static mixer 45.

  The coating gun 30 includes a main body (not shown) and a rotary atomizing head 32 that is rotatably provided on the main body.

The main body has a cylindrical shape, and includes a paint supply pipe 41 for supplying paint to the rotary atomizing head 32, a solvent supply pipe 42 for supplying solvent to the paint supply pipe 41, and a rotary atomizing head by air fed from a compressor. An air motor (not shown) that rotates 32 and a high voltage generator (not shown) that charges the paint are provided.
The rotary atomizing head 32 is formed with an expanded surface 321 that expands in the injection direction.
The paint supply pipe 41 extends along the central axis of the rotary atomizing head 32 and reaches the center of the spread surface 321.

The solvent extrusion device 44 includes a cylindrical cylinder 441, a piston 442 provided in the cylinder 441 so as to be slidable, and a servo motor 443 for moving the piston 442 in the axial direction of the cylinder 441. Prepare.
The piston 442 includes a disk-shaped piston main body 444 that contacts the inner peripheral surface of the cylinder 441, and a rod-shaped shaft 445 provided on the piston main body 444 and connected to the servo motor 443.
The piston 442 is a feed screw mechanism, and the servo motor 443 is driven to rotate so that the position of the piston 442 in the cylinder 441 can be adjusted with high accuracy.

FIG. 4 is a diagram showing the relationship between the command value of the discharge amount and the actual measurement value for the gear pump and the solvent extrusion device.
From FIG. 4, it can be seen that the actual discharge amount of the solvent extrusion apparatus corresponds to the command value almost accurately.
On the other hand, it can be seen that the actual discharge amount of the gear pump is smaller than the command value, and when the command value decreases to some extent, it is impossible to discharge.

  The control device 50 controls the gear pump 43, the solvent extrusion device 44, and the coating gun 30 to spray paint from the coating gun 30.

Next, the operation of the painting robots 13 to 16 when the paint is mixed with a solvent for electrostatic painting will be described.
First, the control device 50 closes the valve 422 and opens the valve 421. In this state, the solvent is supplied from a solvent supply source (not shown) to the solvent supply pipe 42, and the cylinder 441 of the solvent extrusion device 44 is filled with the solvent. To do.
Next, the gear pump 43 is driven to supply the paint to the static mixer 45 through the paint supply pipe 41.

  And, when the NV value of the coating film is out of the predetermined range due to high rotation of the rotary atomizing head (higher than the standard coating condition) and / or a small amount of paint supply (less than the standard coating condition), etc. Simultaneously with supplying the paint to the paint supply pipe 41, the valve 421 is closed and the valve 422 is opened to drive the solvent extrusion device 44, so that the solvent is supplied to the solvent supply pipe 42 so that the NV value of the coating film falls within a predetermined range. The paint and solvent are mixed by the static mixer 45.

  Since the rotary atomizing head 32 is rotating, a centrifugal force acts on the mixture of the discharged paint and solvent, and this mixture is further mixed by the rotation of the rotary atomizing head 32, and the expanded surface 321. Move toward the periphery along the surface. When the mixed paint approaches the peripheral edge of the spreading surface 321, the rotary atomizing head 32 rotates at a high speed, so that the centrifugal force acting on the paint becomes considerably large, and the paint has many fine droplets. Separated into a mist. This mist-like paint scatters from the periphery of the spread surface 321 and is applied to the surface of the body 20.

Hereinafter, the operation of the clear painting facility 10 will be described with reference to FIGS.
In this clear coating facility 10, two types of bodies 20A and 20B are mixed and conveyed from upstream. The body 20B is required to have higher smoothness than the body 20A.
First, as shown in FIG. 5, the clear painting facility 10 performs painting of the bodies 20A and 20B. Specifically, the side surfaces of the body 20A are painted by the painting robots 13-16. Further, the upper surface of the front side of the body 20B is painted by the painting robots 11 and 12. Here, only the paint is supplied to the painting robots 11 to 16.

  When proceeding one tact from the state shown in FIG. 5, the clear painting facility 10 paints the rear side surface of the body 20 </ b> A by the painting robots 15 and 16 as shown in FIG. 6. Further, the painting robots 11 to 14 paint the upper surface on the rear side and the side surface on the front side of the body 20B. Here, since the front side surface of the body 20B is painted by the painting robots 13 and 14, the rotary atomizing head 32 of the painting gun 30 of the painting robots 13 and 14 is more than when the side surface of the body 20A is painted. At the same time, the coating robots 13 and 14 are supplied with a solvent in addition to the paint.

  When one tact progresses from the state shown in FIG. 6, as shown in FIG. 7, the body 20 </ b> A is carried out from the clear coating facility 10, and the body 20 </ b> B is newly carried into the clear coating facility 10. Then, the painting robots 13 to 16 paint the side surface of the downstream body 20B already carried in, and the painting robots 11 and 12 coat the front side upper surface of the newly carried upstream body 20B. . Here, since the side surfaces of the body 20B are painted by the painting robots 13 to 16, the rotary atomizing head 32 of the painting gun 30 of the painting robots 13 to 16 has a higher rotation than when the side surfaces of the body 20A are painted. At the same time, the coating robots 13 to 16 are supplied with a solvent in addition to the paint.

  When one tact advances from the state shown in FIG. 7, the clear painting facility 10 paints the rear side surface of the downstream body 20 </ b> B by the painting robots 15 and 16 as shown in FIG. 8. Also, the painting robots 11 to 14 paint the rear upper surface and the front side surface of the upstream body 20B. Here, since the side surfaces of the body 20B are painted by the painting robots 13 to 16, the rotary atomizing head 32 of the painting gun 30 of the painting robots 13 to 16 has a higher rotation than when the side surfaces of the body 20A are painted. At the same time, the coating robots 13 to 16 are supplied with a solvent in addition to the paint.

  When progressing one tact from the state shown in FIG. 8, as shown in FIG. 9, the body 20 </ b> B is unloaded from the clear coating facility 10, and a body 20 </ b> A is newly loaded into the clear coating facility 10. Then, the painting robots 13 to 16 paint the side surface of the body 20B already carried in, and the painting robots 11 and 12 coat the front side upper surface of the newly carried body 20A. Here, since the painting robots 13 to 16 paint the side surfaces of the body 20B, the rotary atomizing head 32 of the painting gun 30 of the painting robots 13 to 16 rotates at a higher speed than when painting the side surfaces of the body 20A. At the same time, the coating robots 13 to 16 are supplied with a solvent in addition to the paint.

  When proceeding one tact from the state shown in FIG. 9, as shown in FIG. 10, the clear painting facility 10 paints the rear side surface of the body 20 </ b> B already carried in by the painting robots 15 and 16. In addition, the painting robots 11 to 14 paint the rear upper surface and the front side surface of the newly loaded body 20A. Here, since the painting robots 15 and 16 paint the side surfaces of the body 20B, the rotary atomizing head 32 of the painting gun 30 of the painting robots 15 and 16 rotates at a higher speed than when painting the side surfaces of the body 20A. At the same time, the coating robots 15 and 16 are supplied with a solvent in addition to the paint.

[Examples and Comparative Examples]
The paint and solvent were supplied to the above-mentioned clear coating equipment, and the relationship between the ratio of the solvent to the paint and the NV value and LW value was examined.

FIG. 11 is a diagram showing the relationship between the rotational speed of the rotary atomizing head and the NV value. FIG. 12 is a diagram illustrating the relationship between the rotational speed of the rotary atomizing head and the LW value.
In FIG. 12, LW (Long Wave) is an index representing the smoothness of the coating film measured by a measuring instrument called Wavescan (manufactured by BYK Gardner). Specifically, the surface of the coating film is irradiated with laser light from this measuring device, the reflected light intensity on the coating film surface is detected, and the optical profile on the coating film surface is detected. Then, the optical file is subjected to a mathematical filter, the structure of the coating film surface is separated for each wavelength, and the measured wavelength is extracted to a certain extent and digitized. It can be said that the lower the LW value, the smoother the surface and the better the appearance.

Without the addition of solvent to the paint, high NV value is out of a predetermined range (range from in FIG. 11 t ₁ to t _2), which is higher LW value.
That is, when the rotational speed of the rotary atomizing head is increased, the paint particles are atomized, the specific surface area of the paint particles is increased, the amount of volatilization of the solvent in the paint is increased, and the NV value of the coating film is increased. Will also rise. As a result, the fluidity of the coating film decreases, the leveling of the paint applied to the surface to be coated becomes insufficient, and the LW value also tends to increase.

On the other hand, when the rotational speed of the rotary atomizing head is increased and a solvent is added to the paint, the NV value is within a predetermined range and the LW value is lowered.
That is, when the rotational speed of the rotary atomizing head is increased, the paint particles are atomized and the specific surface area of the paint particles is increased. However, since the solvent is added, the ratio of the non-volatile content in the coating film is so high. In other words, an increase in the NV value can be suppressed. Therefore, since the paint applied to the surface to be coated can be leveled without losing fluidity, unevenness on the surface of the coating film is suppressed, and the LW value tends to decrease.

  As described above, the NV value of the coating film is controlled so as not to increase beyond the predetermined range, and the LW value is decreased by increasing the rotational speed of the rotary atomizing head 32 and atomizing the paint particles. It can be seen that the appearance can be improved.

According to this embodiment, there are the following effects.
(1) The solvent extrusion device 44 was driven to adjust the supply amount of the solvent so that the NV value of the coating film formed on the surface to be coated was within a predetermined range. By keeping the NV value of the coating within a predetermined range, the properties of the mixed paint can be controlled, so that the fluidity of the paint applied to the surface to be coated can be secured, and the appearance of the painted surface is highly smooth. Can be obtained.

  (2) The solvent was supplied using a cylinder type solvent extrusion device 44 in which a piston 442 driven by a servo motor 443 was installed. Since the solvent extrusion device has a structure that can control a small discharge amount with high accuracy, the properties of the paint can be managed reliably.

  (3) Since the paint and the solvent are mixed in the vicinity of the coating gun 30 by the combination of the static mixer 45 and the rotary atomizing head 32, compared with the case where the paint and the solvent are mixed in the paint circulation tank, A paint having a desired NV value can be supplied without time lag.

It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.
For example, in the present embodiment, the electrostatic coating apparatus and the electrostatic coating method are applied to the clear coating facility 10, but the present invention is not limited thereto. In other words, it may be applied to intermediate coating equipment, or it may be applied to equipment other than the base coating equipment, such as overcoat clear painting equipment (premium clear painting applied over clear painting). You may apply. Moreover, you may apply to one of these facilities, and may apply to multiple.

  In this embodiment, the solvent and the paint are mixed by the static mixer 45 before being supplied to the rotary atomizing head 32. However, when the kind of paint is changed during the painting, the coating gun 30 is applied from the static mixer 45. Up to the mixed paint must be discarded. Therefore, for example, as shown in FIG. 13, the paint supply pipe 41 may not be provided with a static mixer, and the solvent supply pipe 42 may be connected to the coating gun 30 instead of the static mixer. The same effect as in the above (1) and (2) can be obtained also in the bell tip mixing by the rotary atomizing head.

10 Clear coating equipment (electrostatic coating equipment)
20 Body (surface to be painted)
41 Paint supply pipe (paint supply means)
42 Solvent supply pipe (solvent supply means)
43 Gear pump (paint supply means)
44 Solvent extruder (solvent supply means)
45 Static mixer (mixing means)
50 Control device (control means)
442 Piston 443 Servo motor

Claims (4)

The paint supply means for supplying the paint, the solvent supply means for supplying the solvent, the mixing means for mixing the paint supplied from the paint supply means and the solvent supplied from the solvent supply means, and the mixing means An electrostatic coating apparatus comprising: a rotary atomizing coating apparatus that sprays a paint and a solvent, and a control means that controls these,
The control means drives the solvent extruding means to adjust the supply amount of the solvent so that the NV value of the coating film formed on the surface to be coated falls within a predetermined range. apparatus. The electrostatic coating apparatus according to claim 1,
The electrostatic coating apparatus according to claim 1, wherein the solvent supply means includes a cylinder-type solvent-extruding device having a piston driven by a servo motor. The paint supply means for supplying the paint, the solvent supply means for supplying the solvent, the mixing means for mixing the paint supplied from the paint supply means and the solvent supplied from the solvent supply means, and the mixing means An electrostatic coating method of electrostatic coating using a rotary atomizing coating device that sprays a paint and a solvent,
An electrostatic coating method characterized in that the solvent supply amount is adjusted by driving the solvent extruding means so that the NV value of the coating film formed on the surface to be coated falls within a predetermined range. In the electrostatic coating method according to claim 3,
An electrostatic coating method characterized in that the solvent supply means includes a cylinder-type solvent-extruding device having a piston driven by a servomotor.

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